The purpose of this investigation will be two-fold: 1. to define the pathogenesis of infant group B streptococcal infection by characterization of host-parasite interactions, and 2. to design methods for early detection, treatment, and prevention of disease. Elucidation of host-parasite interactions will be approached by study of "virulence markers" of the organism such as ability to adhere to humaan mucosal surfaces and host factors promoting adherence, extracellular neuraminidase synthesis by the organism, immunochemical and structural analyses important in the human immune response to infection, and study of other bacteria for the presence of shared antigens. Study of human humoral immune response will be approached by use and comparison of several sensitive serologic assays (RABA, ELISA, opsonophagocytic and mouse protective tests) employing purified type-specific surface antigens from all five serotype strains. Several simple and rapid serologic tests will be developed to allow early detection of group B steptococcal disease in infants. Comprehensive clinical and immunologic evaluation of patients with invasive disease will be performed as well as delineation of seroepidemiologic factors which indicate susceptibility to invasive infection. The mechanism of serum antibody production by neonates will be ascertained by use of a mouse spleen plaque-forming assay. Finally, preparation of human hyperimmune globulins containing type-specific antibodies to all five serotypes of group B streptococci and study of its pharmacokinetics in neonates and adult women could be crucial to prevention of infant disease by means of passive immunoprophylaxis.